Recently, interest has developed in touch and/or proximity-based input systems for electronic devices and computer systems that are capable of recognizing multiple touch and/or hover events simultaneously. Many of these systems, for example those based on mutual capacitance or certain optical sensing arrangements, involve applying periodic stimulus waveforms to a plurality of sense points and detecting sense waveforms that can be related to the periodic stimulus waveform by the amount of touch and/or proximity present at the sense point. In some conventional embodiments, multiple separate stimulus waveforms, each having a unique stimulus frequency, were applied to the sense points. This allowed for a form of noise rejection.
Conventionally, noise rejection was accomplished by a variety of techniques involving combining sample values obtained at each sense point at each of the multiple stimulus frequencies. For example, a simple average (i.e., mean) of the sample values could be taken. The mean of all values can have a very high signal to noise ratio (SNR) in relatively low-noise environments. Alternatives to the mean of all values included weighted mean, median, mode, majority vote, and other parametric and robust statistical measures. While these various other statistical measures resist degradation in the presence of noise, each still can be substantially impaired by noise on one or more channels.